for eg. if you have multiple servers with you, you can configure jboss on each machine. And apache webserver which pass the request to available jboss instance. so that one jboss machine is down, others can serve the request.

JBoss traditionally deals strictly in middle-ware, and so does not offer any true HA services for the database layer. To answer your specific questions:

1) The <ha-tx-local-datasource> & <ha-xa-datasource> perform very rudamentary failover - they only offer failover over new connections. Also, there's no guarantee that the servers in your cluster will all point to the same url at the same time. Additionally, you probably don't want to try to initiate master promotion automatically, since you don't want this to be initiated by multiple servers.

Of the options you listed, pgpool-II is probably the best option, since, though it still maintains a single point-of-failure, its point-of-failure does not also house your data. In general, statement-based replication middleware offers a higher level of availability than master-standby replication, and without the potential for data loss. I've not used the Tungsten suite of products, so I can't offer any recommendations either way.

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